When casement windows are made, there are manufacturing tolerances to the heights of the sash and frame. This can cause the vertical space between the sash and frame (the reveal) to vary by over ⅛ inch. When concealed casement hinges are used, the bottom hinge supports all the sash weight, so the distance between the bottom of the sash and frame is a fixed dimension (the hinge height) and all the variation in sash & frame height shows up as extra clearance between the top of the sash and frame. The extra clearance can be large enough to cause gaps between the upper weatherstripping and its sealing surface and result in leaks. Additionally, a reveal at the top of the sash that is twice as large as at the bottom can cause aesthetic issues and a perception of poor quality.
Sash lifters have been developed to address this problem. One such prior design is disclosed in U.S. Patent Application Publication No. US2008/0168715 A1, said document being hereby fully incorporated herein by reference. Such older designs, however, merely support the bottom of the sash in an attempt to make the bottom reveal a uniform height across the width of the sash (bottom of sash parallel to frame). They are not just adjustable in height. And, as depicted in FIG. 2, because the lifter 100 is located a relatively large distance X from the center of rotation C of the sash 102, it causes a relatively large addition to operating torque as the sash rides up the ramp of the lifter 100.
What is needed in the industry is a sash lifter to equalize the amount of reveal at the top and bottom of a casement window sash, and that is also adjustable to accommodate manufacturing tolerances.